1. Technical Field
This invention relates to the art of shaft balancing, and more particularly to the art of balancing tubular driveshafts for automotive use.
2. Discussion of the Prior Art
Balancing of automotive drivelines is a critical requirement. An automotive driveline is conventionally constructed of a roll-formed and longitudinally welded steel tube, to each end of which is welded a steel yoke (connector) for suitable reception of a universal joint. The steel tube, although manufactured to tight tolerances and specifications, will (i) not be uniformly cylindrical in cross-section and absolutely straight throughout its length, and (ii) have irregularities in wall thickness. Similarly, discontinuities appear in the cast or forged yoke connected to such tube. These material and geometrical irregularities will provide an incongruent mass and incongruent rotation centers causing eccentric loading imbalance; bearing loads, vibration, and vehicle noise will be aggravated by consequent whipping of the driveline resulting from unbalanced weight distribution.
Constructing such drivelines of steel has facilitated balancing. With steel driveshafts and yoke connectors, the standard practice has been to weld small weights to the steel tube, preferably to the ends of the steel tube adjacent or overlapping the connectors. The prior art has attempted to ease balancing steel drivelines by using adhesively applied metal tape, thus distributing the balancing weight over a greater area (see U.S. Pat. No. 4,170,896), and alternatively by use of riveted pads, which rivets pierce the wall thickness of the drive tube (see U.S. Pat. No. 4,887,989). The former is disadvantageous because of the high risk of contaminating the adhesive bond and consequently the strength of attachment; the latter is disadvantageous because of the piercing of the tubular driveline wall which creates an unsealed tube violating automotive requirements. Thus, welding balancing weights has remained the preeminent technique.
Construction of a driveline of aluminum or aluminum-based material makes such preeminent balancing technique unusable. Dense balancing weights, usually of steel or iron, cannot be welded to aluminum; soldering or brazing of such dissimilar materials is not sufficient to provide a secure attachment on an automotive driveline. Less dense weights, such as aluminum, will weld, but must be provided in such large size and mass that proper distribution of the balancing weight is difficult. In spite of the long recognized need for lighter weight material in automotive components, such as by the use of aluminum, the prior art has been unable to create a weldable, economical surface for dissimilar metals on an aluminum driveline assembly. Due to the inability to weld steel to aluminum, attaching a dissimilar balancing weight remains an unsolved problem.
Applicants' early experimental approaches proved inadequate, such as by attaching an iron-based ring to an aluminum driveshaft (tube) by shrink-fitting; not only was the fit not durable and stabilized over the expected life of the driveline, but the cost of shrink-fitting was exorbitant. Applicants have also attempted to use pop riveting of steel weights to an aluminum driveline, but the riveting created an unsealed interior due to rivet penetration and thus permits deterioration more rapidly.